In the fabrication of semiconductor devices, wafers of semiconducting nature, such as silicon wafers, must be processed through a multiplicity of fabrication steps which can amount to several hundred steps for a complicated IC device. For instance, a wafer is normally processed through a variety of fabrication steps which may include oxidation, dielectric layer deposition, stress relief and annealing, ion implantation, planarization, chemical-mechanical-polishing, etc. In each of these processing steps, the wafers are processed either singularly or in batches by loading them into a process machine or a wafer boat that can hold up to 24 wafers and then processing them in a horizontal or in a vertical processing chamber. The wafers can also be processed singularly in fabrication chambers that only process one wafer at a time. In-between the processes, the wafers are stored in a wafer storage cassette. One of such popularly used cassettes can hold up to 24 wafers vertically positioned in the cassette. The wafer must be picked-up by a suitable tool for loading or unloading into or from a wafer storage cassette to either a wafer boat or a process chamber for processing single wafer.
Wafer pick-up tools of various configurations have been designed and utilized for handling wafers in a semiconductor fabrication facility. Since wafers are processed in a clean room environment and cannot tolerate the presence of any contaminants, a wafer pick-up tool must be designed to satisfy this important requirement. It is expected that most mechanical pick-up devices, e.g., a clamping device, would generate contaminants due to its mechanical contact with a wafer surface. Consequently, a pick-up device that utilizes vacuum for contacting and holding the wafer is more desirable. Most commercially available vacuum pick-up devices consist of a handle and a fixed-position pick-up head. One of such device 10 is shown in FIG. 1.
As shown in FIG. 1, the vacuum pick-up head 12 of the pick-up device 10 is used to attach itself by vacuum to the backside of a wafer in order to pick-up the wafer. When the tool is used in a wafer storage device 20, as shown in FIG. 2, mechanical damages such as scratches or breakages can occur to the wafers 22 stored in the wafer cassette 24. In a wafer storage device 20 shown in FIG. 2, the wafers 22 are stacked together in close proximity to each other. For instance, in a typical wafer storage cassette 24 used for storing six inch wafers, the wafer-to-wafer distance is approximately 5 mm. The vacuum pick-up head 12 for the wafer pick-up device 10, even though is designed in a very small thickness, can seriously scratch the wafer when it is inserted in-between the wafers 22 in the wafer cassette 24 in an attempt to pick-up a wafer 22 on its backside. In extreme cases, when the vacuum pick-up head 12 directly collides with an edge of a wafer 22, a breakage of the wafer may occur.
It is therefore an object of the present invention to provide a vacuum pick-up device for semiconductor substrates that does not have the drawbacks or shortcomings of the conventional vacuum pick-up devices.
It is another object of the present invention to provide a vacuum pick-up device for semiconductor wafers that is equipped with a guide member on the device for guiding it on a wafer storage cassette.
It is a further object of the present invention to provide a guided vacuum pick-up device for semiconductor wafers that is equipped with a guide member for slidingly engaging a guide bar on a wafer storage cassette.
It is another further object of the present invention to provide a guided vacuum pick-up wand for semiconductor wafers that is equipped with a guide member which has a window therein to expose a pre-marked number on a guide bar integral with a wafer storage cassette.
It is still another object of the present invention to provide a guided vacuum pick-up wand for semiconductor wafers which is equipped with a guide member for slidingly engaging in Z-direction a guide bar located on a wafer storage cassette.
It is yet another object of the present invention to provide a guided vacuum pick-up wand for semiconductor wafers that is equipped with a guide member which slidingly engaging longitudinally a guide bar on a wafer storage cassette and circumferentially one of a plurality of positioning grooves on the guide bar.
It is still another further object of the present invention to provide a guided vacuum pick-up wand for picking up wafers from a wafer storage cassette that utilizes a vacuum pick-up head that has a thickness smaller than a spacing between two immediately adjacent wafers stored in the wafer storage cassette.
It is yet another further object of the present invention to provide a guided vacuum pick-up wand for picking up wafers from a wafer storage cassette that is equipped with a body portion formed with a guide member for slidingly engaging in a circumferential direction for the wand to move in-and-out of the spacing between two immediately adjacent wafers by engaging a guide pin on the guide member to one of a plurality of positioning grooves provided circumferentially on the guide bar.